Muscular activity in relation to support of the upper extremity in work with a computer mouse

The objective of this study was to compare the effects of using a forearm or wrist support on muscular load in the forearm and neck-shoulder region during work with a computer mouse. Fourteen 35- to 50-year-old healthy women who worked with a video display unit for at least 4 hr a day in an office and who also used a computer mouse for at least 2 hr a day participated in this experimental study. In the laboratory, computer mouse use with the forearm supported was compared with computer mouse use with the wrist supported. The participants edited a text table by moving symbols from one square to another in a fixed order. Each trial was a set of 64 movements. The trials were repeated 10 times in random order, 5 trials with each method of support. The dependent variable was electromyographic activity measured from muscles in the preferred lower arm and in the neck-shoulder region. Normalization to the individual mean of each participant was found to be more effective in reducing the interindividual variation than normalization to the maximal electrical activity (MEMG) obtained during isometric maximal voluntary contraction using the variation coefficient. The amplitudes normalized to the individual mean of each participant were used to evaluate the statistical significance of the difference between the methods of support. To interpret the magnitude and the practical meaning of the statistically significant differences, the corresponding mean percentages of the MEMG were used. The results of the study indicate that changing the position and support of the upper extremity affects muscular activity in the forearm and neck-shoulder region. The load on the trapezius muscle is significantly lower when the forearm is supported, and therefore such support may offer one means of preventing common disorders in the neck-shoulder region in office work. The load on the infraspinatus muscle and on forearm flexor muscles was, on the contrary, higher when the forearm was supported. The result may indicate the difficulty that workers have in adopting new hand and upper arm movements when using a computer mouse.